Granular ion exchange process for pulp treatment



Nov. 6, 1962 F. o. READ ETAL. 3,062,738

GRANULAR ION EXCHANGE PROCESS FOR PULP TREATMENT 2 Sheets-Sheet 1 Filed Jan. 15, 1959 a F l I I I I l ||"HHHH 1 ||||I| llllll 2 0 0 2 0 Z 0 5 w w 7 w I I l I I I I I l Ir! l l l I I IIJ. l I t I l I I I I I I II 9 n -ELI l hunv iI I 1- -1-1- q wv I fl H m m my 1 9? V v f v w 2 5 l l l l l l I l llltllllllTlllllllllllDllllllllllllWlllllll a T VI N m V Y E w w 5% A 7 g Nov. 6, 1962 F. o. READ ETAL GRANULAR ION EXCHANGE PROCESS FOR PULP TREATMENT Filed Jan. 15, 1959 2 Sheets-Sheet 2 EXC/IAA/GER NUMBER .fl/vEA/mes E 4 /l/( d F5791) United States Patent Gflhce 3,002,733 Patented Nov. 6, 1962 3,062,738 GRANULAR llGN EXCHANGE FRO CES FUR PULP TREATMENT Frank 0. Read, Ernest H. D. Carman, Harry E. Cross,

and Alexander Thompson Moir, all at .iohannesburg, Transvaal, Republic of South Africa, assignors, by mesue assignments, to The Consolidated Goid Fields of South Africa Limited, London, Engiand, a company of the United Kingdom Filed Jan. 13, 1959, Ser. No. 786,575

Claims priority, application Republic of South Africa .Ian. 31, 1958 11 Claims. (Cl. 210-24) This invention relates to ion exchange processes.

It has been proposed to eitect ion exchange between pulps and ion exchange materials in granular form by contacting the pulp with ion exchange material and then removing the granules of ion exchange material from the pulp.

In one proposal granules of ion exchange resin are made to settle out of a mixture while decanting the pulp. In a second proposal ion exchange resin is contained in baskets which are immersed in the pulp. In yet another proposal the resin is contained in a column through which the pulp is caused to flow upwards.

In all these processes operation is only possible with very low density watery pulps from which substantially all the +325 mesh Tyler fraction has previously been removed and washed by means of a series of classifiers or cyclones and thickeners working in counter-current. This in itself is a comparatively expensive process and some soluble losses of the metal being recovered are inevitable.

Apart from the above proposals it is conventional to filter pulps prior to the ion exchange process. If filtration is resorted to, there is a loss of the dissolved material in the filtering step. This loss may be as high as in uranium recovery plants. To this must also be added the loss due to the inefliciency of the ion exchange process, which may be 1%. The capital cost of the filtration step, particularly if the pulp is acid, may be very high.

An object of the invention is to provide a process which is simple and comparatively cheap to operate and which will be low in capital outlay. In the invention both filtration and desanding are dispensed with and soluble losses outlined above are avoided while loss of ion exchange material is low.

A process according to the invention consists in mixing a pulp with a granular ion exchange material having a specific gravity less than that of the pulp, allowing the mixture to separate into fractions and removing the lighter fraction of the separated mixture containing the ion exchange material.

In a preferred form of the invention the pulp and ion exchange material are continuously introduced at the top of a mixing vessel, such as a Pachuca tank. The mixture overflows at a high level in the vessel into a separator, where under quiescent conditions the ion exchange material floats, and the residual pulp is withdrawn from below.

Conveniently the vessel and the separator are so arranged that the head of pulp in the vessel causes the ion exchange material in suspension in the removed fraction to flow up a column formed at the top of the separator. A series of vessels and separators may be arranged to treat the liquid continuously with the ion exchange material fiowing in counter-current to the liquid.

Where the specific gravity of the resin is between 1.1 and 1.2 it is preferred that the specific gravity of the liquid be kept between 1.4 and 1.5.

An embodiment of the invention is described hereunder and illustrated in the accompanying drawings, in which FIGURE 1 is a diagrammatic side view of apparatus suitable for carrying out the processes of the invention,

FIGURE 2 is a section of the line 22 of FIGURE 1.

FIGURE 3 is a plan view of a convenient lay-out alterenative to FIGURE 1,

FIGURES 4 and 5 are graphs illustrating a specific example of the invention.

The apparatus shown in FIGURE 1 comprises a series of twelve Pachuca tanks 101, 102 to 113, each of which comprises a conical base 100 with an air inlet 201, 202 to 213, and a central column 301, 302 to 313 adjustable in height, in the well-known manner. Adjacent pairs of the Pachuca tanks 101, and 102 and so on are connected together by means of separators consisting in inclined pipes 401, 402 to 412. These pipes are connected to one Pachuca tank of the pair at a high level and the other of the pair at a low level. As shown in FIGURE 2, the pipes 401, 402 communicate with the tanks 101, 102 through small apertures 98 and 99. At the top of each pipe 401 to 412 there is a conduit 501 to 512, which leads upwardly. Below the conduit there is a small pipe 601, 612 through which air is introduced.

Consider the first tank in FIGURE 1, that is the one on the extreme left. Pulp is introduced at the top through pipe 97. It is agitated in the well-known manner in the Pachuca tank 101. Ion exchange material is introduced through the conduits 501, 502 into each tank from the next succeeding tank. The ion exchange material and the pulp are thus intimately mixed. Part of this mixture overflows continuously into the separators 401, 402 through apertures 99, and, under quiescent conditions, ion exchange material floats in the separators 401, 402 and reaches conduits 501, 502. Flow of ion exchange material is assisted by the air introduced through the pipes 601, 602.

Pulp from which ion exchange material has been removed passes into the second tank 102, where it is mixed with ion exchange material introduced at the top from the next succeeding separator 403, and so the process goes on. Any number of tanks may be provided. In the drawings twelve are illustrated. The number will depend on various conditions, which will be apparent to the persons skilled in the art. At the end of the series there is a Pachuca tank 113 which serves as a level controller with the aid of an adjustable pipe 96. Fresh ion exchange material may be introduced into the tank before the overflow regulating tank 113, or into the tank preceding that one. As shown a pipe feeds tank 112.

Obviously if the tanks 101, 102 are arranged in one line, the line may become inconveniently lengthy. For this reason a lay-out such as that shown in FIGURE 3, may be convenient. Here the tanks 101 to 113 are arranged in two staggered rows with the connecting separators 401, 412 between the two rows as shown.

In an example of the invention a pulp obtained from. a typical uranium recovery plant we treated with an anion exchange resin to recover dissolved uranium. The details of this example are as follows:

Plant.-The plant consisted of 12 mixing tanks and one additional tank for level controlling.

The contents of each of these tanks was agitated by introducing air through pipes corresponding to the pipes 201, 202. The tanks were interconnected by means of inclined separators such as 401, 402 each of which formed an angle of 20 degrees with its respective tank, Each separator was provided with a resin withdrawal pipe, such as 501, 502 and an air jet such as 601, 602 to elevate the separated resin. Internal pipes such as 301, 302 were provided so as to prevent air used for agitation from entering the base of the separators and also to maintain a quiet degree of agitation in the agitators. An adjustable overflow was provided in the level controlhng tank.

Operation-Warm uranium-bearing pulp was fed into mixture of resin and pulp up the conduits. The specific gravity of this resin-pulp mixture was approximately 1.43 and on a volumetric basis contained approximately 130 mls. wet settled resin per litre of mixture. The resin-pulp the first tank of the series at constant rate of 3.9 litres 5 mixture withdrawn was discharged into the next precedper minute. Sufiicient air was bubbled into each tank to ing tank, through the conduit, and so on along the series; provide homogeneous mixing of the pulp. and finally the resin-pulp m1xture discharged from the Relevant details regarding the pulp used are as follows: first conduit was screened through a 60 mesh Tyler screen 8 and the pulp returned continuously to the second tank Specific gravity of Pulp 10 of th series, The resin removed was washed and eluted Specific gravlfy of suspe nded Sohds by conventional methods and eventually returned to the Specific gravity of solution circuit Percent solution m pulp The tank and separator preceding the level-controlling TABLE I tank were provided in order to recover any traces of resin which might not have been completely recovered in t e Grading of Suspended Solids preceding separator. All the pulp discharged was screened Tyler mesh: through a mesh Tyler screen to determine the amount +60 P rcent by Weight Nil of resin lost due to entrainment. This loss Was found to 60+90 -d be of the order of 1 ml. of wet settled resin per 8 hours. 90+200 d0 2 20 After 24 hours of continuous operation, samples of 200+325 "do-nresin and pulp were removed from each agitator, sepa- 325 do 54- rated by screening and filtering and analysed for U 0 TABLE III Agitator No. Feed 101 102 103 104 105 100 107 108 100 110 111 After Elution Soln. U308, g.p.l- .741 .480 .238 .133 .098 .060 .040 .027 .017 .012 .008 .005 Resin U305, g.p.l.

wet settled resiIL--- 26.2 15.2 9.06 7. 04 4.06 3. 44 2.74 2.14 1.68 1.44 1.10 0.50 Temperature, 0-.-- 58 50 40 44 40 39 34 32 31 31 Analysis of solution in feed pulp: The results shown in Table III are graphically illus- "grams/litre 1.70 trated in FIGURES 4 and 5. Fe+++ d0 1. 35 As can be seen, the efilciency of ion exchange is H 80 do 3- 0 99.33% which compares favourably with conventional ion Si0 do 2-07 exchange processes. As there has been no filtration there U 0 do 0.741 are no filtering losses. Furthermore, the pulp from the N0 do 0.372 leaching step has not been excessively diluted, and the pH value 1.42 normal ratio of one part of solids to one part of liquid Pulp fiowed through the interconnecting separators and i mbore or less mamtamed no prehmma? triiatment eventually overfiowed into the final Overflow pipel By ingween necessary to remove the coarse raction of solids. adjusting the height of this pipe the pulp levels in the 1 if i tanks could be varied at Wm n 1011 exchange process consisting 1n m1x1ng a pulp For this particular test the level of the final overflow wlthf Fi g g i speclitic pipe was so adjusted as to provide a combined volume gray! y an o Pu Owmg. 6 mixture. 0 separate into fractions and removing the lighter fraction of approximately 80 litres in each stage, 1.e. tank plus of the Se arated mixture containin the ex ha 6 separator of each pair. The average retention time of the material p g 1 n c ng g g g aach stage therefore approxlmately 20 2. The process claimed in claim in which the pulp Initially 1.6 litres of wet settled resin in the nitrate form 2 excfhange- {mammal i con-tmuously lgtrofiuced was added to the pulp in each tank. Thereafter eluted a Op 0 mlxmg V658? he mixture over Owmg at resin in the nitrate form was fed continuously into the a l-ngh level vessel mm a Separator whfire under quiescent conditions the ion exchange material floats tank the second from the end (the level-controlling tank to the to d th l I d f b l luded) at a constant rate of 0.080 litre wet settled P an ares} ua P W1 raw]? mm c a t Th d th t M d thn 3. The process claimed in clalrn 2 in which the vessel of b R h d H i 3 0 a1 f thi i 1n the vessel causes the ion exchange material in suspeny 0 m an e g n ysls 0 s r I SlOIl in the removed fraction to fiow up a conduit formed was as follows TABLE H at the top of the separator.

6 4. The process claimed in claim 3 in which the flow Tyler screen mesh: Percent by weight retained of ion exchange material is assisted by a pump.

+10 Nil 5. The process claimed in claim 3 in which the flow of -l0+l6 11 ion exchange material is assisted by injecting gas into the 16+20 76 conduit. 20+30 11 6. The process claimed in claim 1 in which the specific -30 2 gravity of the ion exchange material is between 1.1 and 1.2 and in which the specific gravity of the pulp is between 'The degree of agitation in each tank was sufficient to 1.4 and 1.5. keep the resin homogeneously mixed with the pulp. 7. An ion exchange process for treating a pulp con- The resin and pulp mixture from each tank overflowed sisting in flowing a granulated ion exchange material havinto its associated separator. As no agitation took place ing a specific gravity less than that of the pulp through in the separators and due to the difference in specific a series of alternate mixing and separating stages in gravity between the resin beads and the pulp, the resin counter-current wtih one another, so that the material collected near the extremity of the resin withdrawal pipe. and the pulp become mixed in the mixing stages, the mix- Sufiicient air was admitted to act as an airlift to lift this tures being allowed to separate into fractions in the separating stages, and including the steps of removing the lighter fraction containing the ion exchange material of a separated mixture in each separating stage and adding it to the next but one mixing stage in the direction of flow of the pulp.

8. The process claimed in claim 7 in which a pulp having a specific gravity of between 1.4 and 1.5 is treated with a granular ion exchange material having a specific gravity of between 1.1 and 1.2.

6 1 1. The process claimed in claim 9 in which the specific gravity of the ion exchange material is between 1.1 and 1.2 and the specific gravity of the pulp is between 1.4 and 1.5.

References Cited in the file of this patent UNITED STATES PATENTS 2,742,381 Weiss et a1. Apr. 17, 1956 FOREIGN PATENTS 780,406 Great Britain July 31, 1957 OTHER REFERENCES Chemical Week, 80, #13, pages 73-79, Mar. 30, 1957.

Chemical and Engineering News, page 80, Sept. 9, 1957.

Davis et al.: Chem. Eng. Progress, April 1954, pages 188197. 

1. AN ION EXCHANGE PROCESS CONSISTING IN MIXING A PULP WITH A GRANULAR ION EXCHANGE MATERIAL HAVING A SPECIFIC GRAVITY LESS THAN THAT OF THE PULP, ALLOWING THE MIXTURE TO SEPARATE INTO FRACTIONS AND REMOVING THE LIGHTER FRACTION OF THE SEPARATED MIXTURE CONTAINING THE ION EXCHANGE MATERIAL. 